The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, HDDs have been desired to store more information in its limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
The further miniaturization of the various components, however, presents its own set of challenges and obstacles. As higher recording densities have been adopted for magnetic recording, tunneling magnetoresistance (TMR) films have come to be used in read sensors of HDDs, which has resulted in improved sensor performance (such as output, signal-to-noise ratio (SNR), etc.). Furthermore, improvements in the film structure have been achieved which has further improved sensor performance. The TMR film structure typically includes an antiferromagnetic layer/ferromagnetic layer/non-magnetic insulating layer/magnetization free layer. The magnetization of the ferromagnetic layer is fixed by the exchange coupling magnetic field generated at the interface of the ferromagnetic layer and the antiferromagnetic layer. Also, the relative direction of magnetization of the magnetization layer comprising the magnetization free layer is changed due to inversion of the magnetization of the external magnetic field. In addition, the magnetic field is detected by the change in electrical resistance produced when current flows perpendicular to the surface of the TMR film.
If the sensor size is simply made smaller to accommodate the higher recording densities, the sensor output drops and noise increasingly occurs, making it difficult to read the signal recorded on the magnetic recording medium. Accordingly, further improvements in sensor structure design that allow for improved sensor output would be greatly beneficial.